1. Field of the Invention
The present invention relates to a method of making an oxide barrier layer for a spin tunnel junction and, more particularly, to implementing oxidation of a metal that forms a barrier junction without surface contamination.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotatable magnetic disk, a slider with write and read heads supported by a suspension arm above the disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider to cause the slider and the write and read heads to ride on an air bearing a slight distance from the surface of the rotating disk. During rotation of the disk the write head writes magnetic bits of information to the disk and the read senses the magnetic bits from the disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A magnetic gap is formed between the first and second pole piece layers by a write gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field across the gap between the pole pieces. This field fringes across the gap at the ABS for the purpose of writing the aforementioned magnetic bits in circular tracks on the rotating disk.
The read head includes a sensor which senses the aforementioned magnetic bits from the rotating disk. One type of sensor is a spin tunnel junction sensor which includes an oxide barrier layer between a ferromagnetic pinned layer and a ferromagnetic free layer. The pinned layer is located on, and exchanged coupled to, an antiferromagnetic layer which pins a magnetic moment of the pinned layer in a first direction which is typically perpendicular to the ABS. The free layer has a magnetic moment which is free to rotate in response to magnetic fields from the rotating disk. A tunneling current I.sub.T is conducted through the spin tunnel junction sensor in a direction perpendicular to the surface planes of the layers. Because of a magnetoresistive affect between the free and pinned layers there is a change in resistance of the spin tunnel junction sensor as a function of cos .theta., where .theta. is the angle between the magnetic moments of the pinned and free layers. When the magnetic moment of the free layer is parallel to the magnetic moment of the pinned layer the resistance to the tunneling current is at a minimum, and when these moments are antiparallel with respect to one another the resistance to the tunneling current is at a maximum. Accordingly, as the tunneling current I.sub.T is conducted through the tunnel junction sensor, an increase or decrease in the resistance of the sensor causes a change in potential in the aforementioned processing circuitry. The processing circuitry employs these potential changes to produce readback signals.
In order for the tunneling effect to work properly the oxide barrier layer must be extremely thin, such as 10 .ANG.-20 .ANG. thick. The barrier layer must be smooth and uniform with a low defect density and a large dielectric strength. Aluminum oxide (Al.sub.2 O.sub.3) is the most commonly used barrier material. There is a strong-felt need to provide a method of making the barrier layer for a tunnel junction sensor that has the aforementioned attributes.